Long-term stability analysis of loess cutting shallow slope based on wet-dry cycle test
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摘要: 为评估干湿循环作用对黄土边坡浅层土体强度的劣化效应，对甘肃定西Q3原状黄土开展了不同干湿循环路径下的室内直剪试验，分析干湿循环次数、循环幅度与下限含水率对土体抗剪强度的影响，建立了考虑干湿循环三参数的强度劣化模型，并运用强度折减法对比了不同干湿循环路径下黄土路堑浅层边坡的长期稳定性。试验结果表明：随着干湿循环次数增加，原状黄土的黏聚力呈现先减小后趋于稳定的变化趋势，可采用双曲线函数进行拟合，内摩擦角呈线性下降趋势，10次干湿循环后，原状黄土黏聚力与内摩擦角的最大劣化度分别为27.64%与9.88%；在相同干湿循环次数下，循环幅度对原状黄土黏聚力和内摩擦角的劣化效应大于下限含水率；干湿循环过程中黄土路堑浅层边坡的长期稳定性系数遵循指数下降函数，不同干湿循环路径下边坡稳定性系数最大降幅为61.5%，且在6次循环后稳定性系数降幅约占总减小值的85%；干湿循环中循环幅度和下限含水率影响着黄土路堑浅层边坡稳定性，表现为随着下限含水率增大，浅层边坡稳定性系数先增大后趋于稳定，但随着循环幅度增大，稳定性系数线性减小；工程实际中边坡不同深度土体含水率变化范围不同，干湿循环路径存在差异，在进行黄土路堑边坡长期稳定性分析时建议考虑土体的干湿循环分层效应。Abstract: To evaluate the shallow soil strength deterioration effect of loess slope under wet-dry cycle, the laboratory direct shear tests were carried out under different wet-dry cycle paths on Q3 undisturbed loess from Dingxi, Gansu Province. The effects of cycling times, cycling amplitude and lower bound water content on the shear strength of the soil were analyzed. A strength degradation model considering three parameters of wet-dry cycle was established, and the long-term stabilities of loess cutting shallow slope under different wet-dry cycle paths were compared by the strength reduction method. Test results show that the cohesion of undisturbed loess first decreases and then tends to be stable with the increase of wet-dry cycles, which can be fitted by the hyperbolic function. The internal friction angle decreases linearly. After 10 cycles, the maximum deterioration degrees of cohesion and internal friction angle are 27.64% and 9.88%, respectively. Under the same wet-dry cycles, the degradation effects of the cycling amplitude on the cohesion and internal friction angle of undisturbed loess are greater than that of the lower bound water content. The long-term stability coefficient of loess cutting shallow slope follows an exponentially decreasing function during the wet-dry cycle. The maximum reduction of slope stability coefficient under different wet-dry cycle paths is 61.5%, and the reduction of stability coefficient accounts for 85% of the total reduction after 6 cycles. The stability of loess cutting shallow slope is affected by the cycling amplitude and lower bound water content in the wet-dry cycle, which shows that the slope stability increases first and then tends to be stable with the increase of lower bound water content. However, with the increase of cycling amplitude, the stability coefficient decreases linearly. In engineering practice, the water content varies with the depth in the slope, and the wet-dry cycle paths are different, so the layering effect of wet-dry cycle should be considered in long-term stability analysis of loess cutting slope.
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Key words:
- subgrade engineering /
- cutting slope /
- undisturbed loess /
- wet-dry cycle /
- deterioration degree /
- stability analysis
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图 5 干湿循环下原状黄土强度劣化规律
Figure 5. Strength deterioration laws of undisturbed loess under wet-dry cycle
图 6 试验结束后各路径作用下土样的裂隙发育
Figure 6. Crack development of soil samples under different paths after test
图 7 劣化度参数与循环路径参数的关系
Figure 7. Relationship between deterioration degree parameters and cycling path parameters
图 10 边坡稳定性系数与干湿循环路径的关系
Figure 10. Relationship between slope stability coefficients and wet-dry cycle paths
图 11 边坡稳定性系数与干湿循环次数的关系
Figure 11. Relationship between slope stability coefficients and number of wet-dry cycles
图 12 黄土边坡干湿循环分层效应剖面
Figure 12. Profile of layering effect of wet-dry cycle on loess slope
表 1 原状黄土干湿循环试验方案
Table 1. Wet-dry cycle test schemes of undisturbed loess
试验编号 试验路径 干密度/(g·cm-3) 循环路径 干湿循环次数 1 A 1.35 5%→15%→5% 10 2 B 10%→20%→10% 3 C 15%→25%→15% 4 D 5%→25%→5% 
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表 2 原状黄土强度劣化度参数
Table 2. Strength deterioration degree parameters of undisturbed loess
试验路径 参数 M/% N R2 A c 28.06 2.239 0.998 φ 0.983 0.992 B c 23.10 3.078 0.993 φ 0.922 0.974 C c 17.16 1.599 0.996 φ 0.681 0.988 D c 36.07 2.658 0.997 φ 1.131 0.963
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表 3 土体物理力学参数
Table 3. Physical and mechanical parameters of soil
干密度/(g·cm-3) 饱和渗透系数/(cm·s-1) 弹性模量/MPa 初始黏聚力/kPa 初始内摩擦角/(°) 1.35 1.08×10-4 14 19.1 26.6
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